Sapphire is a gemstone variety of corundum (Al₂O₃) that occurs in various colors except red, which is classified as ruby. It has a Mohs hardness of 9, making it one of the hardest naturally occurring minerals, second only to diamond and moissanite. The blue variety, caused by trace amounts of iron and titanium, is the most well-known, but sapphires can also appear in yellow, green, pink, purple, and colorless forms. Major sources include Sri Lanka, Myanmar, Madagascar, Thailand, and Australia, with Kashmir sapphires being particularly prized for their deep, velvety blue color. Sapphires exhibit pleochroism, fluorescence in some cases, and a strong resistance to scratching and abrasion, making them ideal for fine jewelry and industrial applications.